Math you learned in elementary school (hopefully using our Excel Math curriculum) should be adequate for you to monitor your own nutritional intake.
RDA is part of a larger scheme called the Dietary Reference Intake. The Dietary Reference Intake recommendations for US and Canadian citizens include:
- Estimated Average Requirements (EAR) - the amount of food that should satisfy 50% of the people in a specific age or gender group. EAR is determined by a committee reviewing recent scientific literature.
- Recommended Dietary Allowances (RDA) - the daily quantity of a substance which the Food and Nutrition Board feels will meet the needs of virtually all (97–98%) healthy individuals. It is approximately 20% higher than the EAR.
- Adequate Intake (AI) - used where no RDA has been established. This amount is felt to be barely adequate for everyone in a demographic group.
- Tolerable Upper Intake Levels (UL) or Acceptable Daily Intake (ADI) - these are ceiling levels, to prevent excessive intake of nutrients (like vitamin A or D) that can be toxic. This is the highest level of daily consumption that is unlikely to cause side effects when taken long term, without medical supervision.
NOTE: The DRI levels cover only what we feed ourselves. Other substances ingested due to packaging, contamination, pesticides, spoilage, etc. are measured in terms of cumulative contact or consumption over a long period of time.
In the case of Vitamin D, yesterday's topic, we each have a different ability to synthesize it from the sun exposure and diet. We live in varying places on the globe, have differing amounts of clothing on when we go outdoors, have unique skin coloration and blocking abilities, etc.
Even in Sunny Southern California, many people have low vitamin D levels because we have become very careful about sun exposure (causing skin cancer), and we don't drink as much milk as we used to (fortified with vitamin D). In theory, the RDA of 600 IUs of vitamin D should be adequate to maintain bone health and calcium metabolism, but due to low levels in many people in the USA, there is ongoing debate about raising the RDA.
Although sunlight is a major source of vitamin D for some, the vitamin D RDAs assume minimal sun exposure. If you want to enhance your own Vitamin D levels through sunshine, be aware that cloud cover reduces UV energy by 50% and shade reduces it by 60%. Window glass and sunscreens of SPF 8 or higher block all vitamin D production.
As described yesterday, it's possible to buy supplements to assist your body with its normal intake or production of vitamin D. So now we know that we can obtain vitamin D through diet, sun or supplements, but how do we know if we have been making or taking enough?
current recommendations from the National Institutes of Heath; the numbers represent nanograms per milliliter of 25-hydroxyvitamin D:
|D Level||Health Status & Consequences|
|< 30||Deficiency, leading to rickets and osteomalacia; possible connections to heart disease, asthma or cancer|
|30–50||May be inadequate for bone and overall health in healthy individuals|
|50–80||Considered adequate for bone and overall health in healthy individuals|
|> 125||Possible that there may be adverse effects from levels this high|
My tests said I had a level of 12-15. That's far too low, so I was prescribed Vitamin D supplements. After 50,000 IUs per week for 3 months to catch up, my doctor told me to take 1000–2000 IUs per day and get outdoors more often. A follow-up test shows my vitamin D level is approaching 50.
My health care provider told me that one-third of Americans have low vitamin D levels, and many people are being asked to improve their diet and sun exposure or take supplements. Your doctor might have the same advice for you, and now you know the math you need to monitor yourself.
PS - I am taking a week or so off this blog so I can go outside and get my Vitamin D levels up ... and read through Wikipedia's Vitamin D page.